This invention relates generally to accumulation conveyors and to conveyor systems incorporating such accumulation conveyors. More particularly the invention relates to pneumatically controlled accumulation conveyors. The invention is especially useful with conveyor systems having sortation means and accumulation conveyors outbound of the sortation means.
Newer warehouse conveyor systems are called upon to process inventory at an ever increasing rate of throughput. In other words, the industry standard for product throughput increases almost yearly. In order to meet these demanding specifications, designers typically increase line speeds. However, as line speeds become progressively higher, increasing them further comes at an ever increasing cost. Special bearings are required for the myriad of power rollers and line noise becomes a more significant problem. Therefore, the need exists for techniques to increase system throughput without a commensurate increase in line speed.
In warehouse conveyor systems, outgoing product is sorted at a sortation conveyor into orders destined for particular customers. Each order is typically diverted to a sortation spur designated by the conveyor management system for that customer and from the spur to a holding area or directly to a transportation vehicle. As long as product is fairly well mixed, each spur will receive product at a rate that is roughly equal to the rate at which the product is discharged at the end of the outbound conveyor. However, situations arise where a large number of consecutive, or closely grouped, products are designated for one spur, which momentarily increases the rate at which products are fed into the outbound conveyor. In order to accommodate the variation in product feed rate, the outbound conveyor typically has had to run at exceptionally high rate.
Various forms of accumulation conveyors are known in the art. An automatic pneumatically controlled accumulation conveyor is disclosed in commonly assigned U.S. Pat. No. 3,768,630 issued to Russell A. Inwood et al. for an ACCUMULATOR WITH AUTOMATIC OVERRIDE in which groups of selectively powered rollers are organized into zones and each zone is controlled by an actuator responsive either to a sensing roller positioned within the zone or to a clear-out valve. In an accumulation mode, a case stop is raised and cases accumulate behind the stop. Cases continue to move toward downstream zones until they accumulate to the point of actuating a sensing roller. When this occurs, the associated zone is de-activated such that cases in that zone are no longer propelled. In a clear-out mode, a clear-out valve is actuated in order to power all of the zones and the case stop is lowered to propel the cases off of the accumulating conveyor.
While the Inwood et al. '630 patent recognized the desirability of keeping articles closely spaced, it accomplished the result using a shuttle valve associated with each zone which received its operating pressure in the appropriate circumstances from a series path extending through one or several downstream shuttle valves. During a clear-out mode, all zones are actuated through such series path. The result is a sluggish response to changes in operating condition. Furthermore, such accumulation conveyor is taught in Inwood et al. for use in an application in which articles would accumulate behind a case stop until cleared out in a "slug" by a clear-out command from a central control system. While such function is useful in the product input portion of a conveyor system, it does not solve the problem attendant to the sortation systems in which product may be received in slugs but which need to be discharged at a controlled, generally constant, rate.